[pylint] Recurse into subscript subexpressions when searching for l…

…ist/dict lookups (`PLR1733`, `PLR1736`) (#13186)

## Summary

The `SequenceIndexVisitor` currently does not recurse into
subexpressions of subscripts when searching for subscript accesses that
would trigger this rule. That means that we don't currently detect
violations of the rule on snippets like this:

```py
data = {"a": 1, "b": 2}
column_names = ["a", "b"]
for index, column_name in enumerate(column_names):
    _ = data[column_names[index]]
```

Fixes #13183

## Test Plan

`cargo test -p ruff_linter`

crates/ruff_linter/resources/test/fixtures/pylint/unnecessary_dict_index_lookup.py

@@ -38,3 +38,16 @@ def value_intentionally_unused():
         print(FRUITS[fruit_name])  # OK
         blah = FRUITS[fruit_name]  # OK
         assert FRUITS[fruit_name] == "pear"  # OK
+
+
+def rewrite_client_arrays(value_arrays: dict[str, list[int]]) -> dict[str, list[int]]:
+    """Function from https://github.com/zulip/zulip/blob/3da91e951cd03cfa0b9c67378224e348353f36a6/analytics/views/stats.py#L617C1-L626C25"""
+    mapped_arrays: dict[str, list[int]] = {}
+    for label, array in value_arrays.items():
+        mapped_label = client_label_map(label)
+        if mapped_label in mapped_arrays:
+            for i in range(len(array)):
+                mapped_arrays[mapped_label][i] += value_arrays[label][i]  # PLR1733
+        else:
+            mapped_arrays[mapped_label] = [value_arrays[label][i] for i in range(len(array))]  # PLR1733
+    return mapped_arrays

crates/ruff_linter/resources/test/fixtures/pylint/unnecessary_list_index_lookup.py

@@ -76,3 +76,10 @@ def start():
     # PLR1736
     for index, list_item in enumerate(some_list):
         print(some_list[index])
+
+
+def nested_index_lookup():
+    data = {"a": 1, "b": 2}
+    column_names = ["a", "b"]
+    for index, column_name in enumerate(column_names):
+        _ = data[column_names[index]]  # PLR1736

crates/ruff_linter/src/rules/pylint/helpers.rs

@@ -144,27 +144,25 @@ impl<'a> Visitor<'_> for SequenceIndexVisitor<'a> {
         if self.modified {
             return;
         }
-        match expr {
-            Expr::Subscript(ast::ExprSubscript {
-                value,
-                slice,
-                range,
-                ..
-            }) => {
-                let Expr::Name(ast::ExprName { id, .. }) = value.as_ref() else {
-                    return;
-                };
+        if let Expr::Subscript(ast::ExprSubscript {
+            value,
+            slice,
+            range,
+            ..
+        }) = expr
+        {
+            if let Expr::Name(ast::ExprName { id, .. }) = &**value {
                 if id == self.sequence_name {
-                    let Expr::Name(ast::ExprName { id, .. }) = slice.as_ref() else {
-                        return;
-                    };
-                    if id == self.index_name {
-                        self.accesses.push(*range);
+                    if let Expr::Name(ast::ExprName { id, .. }) = &**slice {
+                        if id == self.index_name {
+                            self.accesses.push(*range);
+                        }
                     }
                 }
             }
-            _ => visitor::walk_expr(self, expr),
         }
+
+        visitor::walk_expr(self, expr);
     }
 }
 

crates/ruff_linter/src/rules/pylint/snapshots/ruff_linter__rules__pylint__tests__PLR1733_unnecessary_dict_index_lookup.py.snap

@@ -121,4 +121,41 @@ unnecessary_dict_index_lookup.py:11:16: PLR1733 [*] Unnecessary lookup of dictio
 13 13 | 
 14 14 | def dont_fix_these():
 
+unnecessary_dict_index_lookup.py:50:51: PLR1733 [*] Unnecessary lookup of dictionary value by key
+   |
+48 |         if mapped_label in mapped_arrays:
+49 |             for i in range(len(array)):
+50 |                 mapped_arrays[mapped_label][i] += value_arrays[label][i]  # PLR1733
+   |                                                   ^^^^^^^^^^^^^^^^^^^ PLR1733
+51 |         else:
+52 |             mapped_arrays[mapped_label] = [value_arrays[label][i] for i in range(len(array))]  # PLR1733
+   |
+   = help: Use existing variable
+
+ℹ Safe fix
+47 47 |         mapped_label = client_label_map(label)
+48 48 |         if mapped_label in mapped_arrays:
+49 49 |             for i in range(len(array)):
+50    |-                mapped_arrays[mapped_label][i] += value_arrays[label][i]  # PLR1733
+   50 |+                mapped_arrays[mapped_label][i] += array[i]  # PLR1733
+51 51 |         else:
+52 52 |             mapped_arrays[mapped_label] = [value_arrays[label][i] for i in range(len(array))]  # PLR1733
+53 53 |     return mapped_arrays
 
+unnecessary_dict_index_lookup.py:52:44: PLR1733 [*] Unnecessary lookup of dictionary value by key
+   |
+50 |                 mapped_arrays[mapped_label][i] += value_arrays[label][i]  # PLR1733
+51 |         else:
+52 |             mapped_arrays[mapped_label] = [value_arrays[label][i] for i in range(len(array))]  # PLR1733
+   |                                            ^^^^^^^^^^^^^^^^^^^ PLR1733
+53 |     return mapped_arrays
+   |
+   = help: Use existing variable
+
+ℹ Safe fix
+49 49 |             for i in range(len(array)):
+50 50 |                 mapped_arrays[mapped_label][i] += value_arrays[label][i]  # PLR1733
+51 51 |         else:
+52    |-            mapped_arrays[mapped_label] = [value_arrays[label][i] for i in range(len(array))]  # PLR1733
+   52 |+            mapped_arrays[mapped_label] = [array[i] for i in range(len(array))]  # PLR1733
+53 53 |     return mapped_arrays

crates/ruff_linter/src/rules/pylint/snapshots/ruff_linter__rules__pylint__tests__PLR1736_unnecessary_list_index_lookup.py.snap

@@ -218,3 +218,22 @@ unnecessary_list_index_lookup.py:78:15: PLR1736 [*] List index lookup in `enumer
 77 77 |     for index, list_item in enumerate(some_list):
 78    |-        print(some_list[index])
    78 |+        print(list_item)
+79 79 | 
+80 80 | 
+81 81 | def nested_index_lookup():
+
+unnecessary_list_index_lookup.py:85:18: PLR1736 [*] List index lookup in `enumerate()` loop
+   |
+83 |     column_names = ["a", "b"]
+84 |     for index, column_name in enumerate(column_names):
+85 |         _ = data[column_names[index]]  # PLR1736
+   |                  ^^^^^^^^^^^^^^^^^^^ PLR1736
+   |
+   = help: Use the loop variable directly
+
+ℹ Safe fix
+82 82 |     data = {"a": 1, "b": 2}
+83 83 |     column_names = ["a", "b"]
+84 84 |     for index, column_name in enumerate(column_names):
+85    |-        _ = data[column_names[index]]  # PLR1736
+   85 |+        _ = data[column_name]  # PLR1736